Sensitizing composition for preparing blue-print paper



Patented July 8, 1924.

UNITED STATES ERNEST BERTSCH, OF HAGUENAU, FRANCE.

Io Drawing.

SENSITIZING COMPOSITION FOR PREPARING BLUE-PRINT PAPER.

Application filed August 29, 1921. Serial No. 496,593.

(GRANTED UNDER THE PROVISIONS OF THE ACT OF MARCH 3, 1921, '41 STAT. L, 1813.)

To all whom it may concern:

Be it known that ERNEST BERTSCH, citizen of France, residing at Haguenau, Alsace, France, has invented certain new and 6 useful Improvements in sensitizing Composition for Preparing Blue-Print Paper (for which I have filed applicationsin Germany,

July 6, 1918; application of addition February 9, 1921; France, March 31, 1921; Den- 10 mark, March 30, 1921 ;'-Sweden, March 31, 1921; Norway, March 31, 1921; Holland, March 31, 1921; and Luxembourg, April 9, 1921), of which the following is a specification.

It is well known that in the production of blue negative light printing papers by the use of ferric salts for example alkali ferric oxalates to add thereto free oxalic acid "so as to permit the white lines to appear more clearly. This result however is not obtained,

but the paper thus produced possesses a series of disadvantages which exclude its possibility as a marketable article. The paper appears grey running into blue and deteriorates rapidly, therefore does not possess any durability. After exposure it does not give pure white lines. During exposure the tone passes from olive green to a dark shade of blue, dark indigo blue to grey blue; 80 when washed the print becomes dark blue and white lines appear which in consequence of the dark blue tone appear blue, but this is not the case. The dark blue colour tone returns when drying so that the print be- 86 comes still more intolerable. Paper .thus obtained cannot be manufactured on a large scale as on the cylinder acid oxalate salts are deposited which can only be dissolved with difliculty and which tear the paper during its production and make it streaky. Th .process is therefore only of slight value as the paper prepared thereby must be exposed directly after its preparation as otherwise it would not produce satisfactory copies.

According to the present invention a neutral alkali oxalate is added to the ferric salt,

preferably at a strength of 10-20%. As an example the following may be mentioned: to 10 kg. of alkali ferric oxalate-as sub stitute for ferric ammonium acetateare added 1; kg. of potassium or sodium oxalate. This salt mixture is then dissolved in '20 to 30 litres of hot water and to the solution is preparation therefore retains its yellow colour unaltered and is durable. On exposare the colour tone passes from ellow to emerald green, a shade of blue, bright blue, yellow grey to a bright yellow grey. After washing the blue colour tone increases in intensity by drying. The lines become snow white on a deep blue ground.

According to the invention the process is carried on a further stage to that wherein 10 to 20% of neutral alkali-oxalate is added to the ferric salts as above described in that mono-acidic oxalate is added whereby the neutral salt is contained in excess in the mixture whilst the acid salt forms only a fraction thereof. In this case the excess of neutral salt in comparison to the monoacidic oxalate produces a preserving effect so that a separate oxidizing agent is unnecessary. I

In preparing this mixture the operation is preferably such that oxalicacid is neutralized by means of alkali or alkali carbonate and then the excess of oxalic acid favourable to the process is added; for example 126 grams of oxalic acid are neutralized by means of alkali or alkali carbonate and then 20 to 25 grams of oxalic acid are added.

The same applies to the potassium salt, sodium salt ammonium salt and other easily soluble oxalate salts. Other acids may citric acid process which in consequence of b used in place of the oxalate salts as addition to the neutral salts and produce a favourable Neutral alkali salts of or i the high price and the difliculty in obtain ing citric acid cannot be carried out efiectively.

Having now particularly described and 5 ascertained the nature of my said invention and in What manner the same is to be performed, I declare that what I claim is 1. A composition for use in the production of blue print paper, comprising organic I 10 ferric salts, and a neutral alkali oxalate.

2. A composition for use in the production of blue print paper, comprising organic ferric salts about ninety per cent, and a neutral alkali oxalate, about ten per cent.

In testimony whereof I hereunto afix my 1 signature in the presence of two Witnesses.

ERNEST BERTSCH.

Witnesses:

FRANK A. K LLER, JOHN A. Scorn 

